Choanal atresia, unilateral

This is the ultrasound scan of a fetus at 15 and 20 weeks of gestation. Actually at first glance, the primary diagnosis was the differential between a single nostril and severe nasal septal deviation. The explanation to "the disappearance of the single nostril" was a mucous plug which deviated the septum lateraly (usually there is no stream of fluid in the obstructed nasal cavity) and for some reason the plug was pumped out or had liqueified towards week 20.